Quasar feedback and the origin of radio emission in radio-quiet quasars

Abstract

We conduct kinematic analysis of the SDSS spectra of 568 obscured luminous\nquasars, with the emphasis on the kinematic structure of the [OIII]5007\nemission line. [OIII] emission tends to show blueshifts and blue excess, which\nindicates that at least part of the narrow-line gas is undergoing an organized\noutflow. The velocity width containing 90% of line power ranges from 370 to\n4780 km/sec, suggesting outflow velocities up to 2000 km/sec. The velocity\nwidth of the [OIII] emission is positively correlated with the radio luminosity\namong the radio-quiet quasars. We propose that radio emission in radio-quiet\nquasars is due to relativistic particles accelerated in the shocks within the\nquasar-driven outflows; star formation in quasar hosts is insufficient to\nexplain the observed radio emission. The median radio luminosity of the sample\nof nu L_nu[1.4GHz] = 10^40 erg/sec suggests a median kinetic luminosity of the\nquasar-driven wind of L_wind=3x10^44 erg/sec, or about 4% of the estimated\nmedian bolometric luminosity L_bol=8x10^45 erg/sec. Furthermore, the velocity\nwidth of [OIII] is positively correlated with mid-infrared luminosity, which\nsuggests that outflows are ultimately driven by the radiative output of the\nquasar. As the outflow velocity increases, some emission lines characteristic\nof shocks in quasi-neutral medium increase as well, which we take as further\nevidence of quasar-driven winds propagating into the interstellar medium of the\nhost galaxy. None of the kinematic components show correlations with the\nstellar velocity dispersions of the host galaxies, so there is no evidence that\nany of the gas in the narrow-line region of quasars is in dynamical equilibrium\nwith the host galaxy. Quasar feedback appears to operate above the threshold\nluminosity of L_bol=3x10^45 erg/sec.\n